The present invention relates broadly to calorimeters, and in particular to a high energy single pulse laser calorimeter apparatus.
Calorimeters for indicating the energy in laser beams must be designed with certain specific characteristics. For example, because of the extremely high concentrated energy in a laser beam, the absorbing material of the calorimeter as well as the volume of the absorbing medium must be such that it will not be damaged by the impingement of the laser beam thereon. It is also important that the medium does not reflect the signal back into the laser which could result in feedback that might damage or destroy the laser itself. In addition, it is important that a relatively high sensitivity be realizable in view of the extremely short period of time of actual impingement of the radiation on the absorbing medium. Normally, a volumetric type of the absorbing medium with a small capacity has greater sensitivity. Finally, it is highly desirable that the calorimeter absorbing medium come to thermal equilibrium as soon as possible after irradiation. If the response time is too slow, the necessity of compensating for energy losses during the lag period must be compensated therefor.
Heretofore, some of the more damage resistant calorimeters have utilized a liquid cell as an absorbing medium. This cell is positioned to intercept the laser radiation and the rise in heat of the liquid in the cell is measured by thermocouples which are connected to the cell and to a reference mass. In order to avoid damage of the cell, it is necessary that it be relatively large and contain a relatively large volume of liquid. This relatively large volume of liquid results in an undesirably long length of time for the liquid to come to thermal equilibrium. By the time equilibrium is obtained so that a proper reading can be taken, some temperature loss has occurred and extrapolation from curves is necessary to correct for the error. Moreover, the sensitivity is somewhat lower than desirable because of the relatively large thermal capacity of the absorbing cell.